750-392
CBEX-DE
2-11
Blowdown - Steam Boilers
When surface or continuous blowdown is not utilized manual blowdown is used to control the dissolved or sus-
pended solids in addition to the sludge. This will involve chemical treatment to sequester the TDS.
In practice, the valve(s) of the bottom blowdown are opened periodically in accordance with an operating sched-
ule and/or chemical control test. From the standpoint of control, economy and results, frequent short blows are
preferred to infrequent lengthy blows. The length and frequency of the blowdown is particularly important when
the suspended solids content of the water is high. With the use of frequent short blows a more uniform concen-
tration of the pressure vessel water is maintained.
In cases where the feedwater is exceptionally pure, or where there is a high percentage of return condensate,
Blowdown may be employed less frequently since less sludge accumulates in the pressure vessel. When dis-
solved and/or suspended solids approach or exceed predetermined limits, manual blowdown to lower the con-
centrations is required.
It is generally recommended that a steam boiler be blown down at least once in every eight-hour period, but fre-
quency may vary depending upon water and operating conditions. The blowdown amounts and schedule should
be recommended by your local Cleaver-Brooks authorized representative.
A hot water boiler does not normally include openings for surface and bottom blowdown since blowdowns are
not practiced. The need remains to be alert to system water losses and corresponding amount of raw water
make-up. A water meter is recommended for water make-up lines.
2.7.3 — Manual Blowdown Procedure
Blowdown is most effective at a point when the generation of steam is at the lowest rate and feedwater input is
also low.
Be sure the blowoff piping and separator tank are in proper operating condition. Discharge vents should be clear
of obstruction, and the waste should be piped to a point of safe discharge.
If a quick opening valve and globe type of slow opening valve are in combination, the former is normally opened
first and closed last with blow down accomplished with the globe or slow opening valve.
When opening the second slow opening valve, crack it slightly to allow the lines to warm, then continue opening
slowly.
The length of each blow should be determined by actual water analysis. Lowering the water in the gauge glass
approximately 1/2” is often acceptable as a guide to adequate blow. However, lowering the water 1/2” should not
be interpreted as a rule since water analysis procedures should prevail. If the glass cannot be viewed by the party
operating the valve, another operator should watch the glass and direct the valve operator.
Close the downstream (slow opening) valve first and as fast as possible. Then close the valve next to the boiler.
Slightly crack the downstream valve and then close it tightly.
Do not pump the lever action valve open and closed, as water hammer is apt to break the valve bodies or pipe fit-
tings. Failure to follow these instructions could cause damage to the equipment.
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Caution
Summary of Contents for CBEX-DE
Page 1: ...CBEX DE Dryback Elite Boiler 250 800 HP Operation and Maintenance 750 392 10 2019 ...
Page 54: ...Preparations for Startup 3 22 750 392 CBEX DE ...
Page 74: ...Startup and Operation 4 20 750 392 CBEX DE ...
Page 104: ...Inspection and Maintenance 5 30 750 392 CBEX DE ...
Page 122: ...Parts 6 18 750 392 CBEX DE 6 11 Temperature Controls Hot Water ...
Page 124: ......